Modern integrated circuit microprocessors and systems-on-chip with data processing cores are able to perform large numbers of computations at relatively high clock speeds. These high speeds can cause the integrated circuit die to heat up significantly. These integrated circuits frequently include on-chip temperature sensors to determine die temperature and to make power management decisions based on how close the integrated circuit die is to its thermal limits. For example when die temperature becomes too high, the speed of the clocks can be lowered or “throttled” so that the circuit can continue to operate properly, albeit at a lower performance level.
On-die temperature can be measured by a variety of circuits. For example the current through a resistor or a semiconductor diode varies with temperature, and the integrated circuit can infer the die temperature by measuring these currents. It is also possible to measure the die temperature using a temperature dependent ring oscillator (TRO). The TRO outputs a clock signal whose frequency is a function of temperature. The frequency of the TRO however is dependent not only on temperature but also on other factors such as manufacturing process variations. Known integrated circuits calibrate the temperature sensors, such as TROs, to obtain a baseline temperature measurement against a standard and then infer the temperature based on the deviation of the measurement from the standard. However it is difficult to perform accurate temperature calibration when the temperature sensors and other circuits in the chip use the same power supply voltage and heat up the die after power is applied and thereby distort the baseline calibration measurement.
In the following description, the use of the same reference numerals in different drawings indicates similar or identical items. Unless otherwise noted, the word “coupled” and its associated verb forms include both direct connection and indirect electrical connection by means known in the art, and unless otherwise noted any description of direct connection implies alternate embodiments using suitable forms of indirect electrical connection as well. Additionally, the terms remap and migrate, and variations thereof, are utilized interchangeably as a descriptive term for relocating.